Microwave Weakening Mechanism And Experimental Study Of Dense Porphyry

As China's main thermal coal production base,Datong Coalfield has a large amount of intrusion of porphyry in coal measures.After the intrusion of porphyry into the coal seam,it will destroy the integrity of the recoverable coal seam,reduce the recoverable thickness of the coal seam,reduce the recoverable reserves of the coal seam,cause waste of resources,and be affected by the intrusion of the porphyry.Significant changes will occur,affecting the value of coal;at the same time,intrusion of porphyry into the coal seam will also affect the safe production of the mine.In the intrusion area of porphyry,the degree of coal metamorphism will increase and the amount of gas adsorbed will increase.The gas concentration in the corners or return air flow will be exceeded;the intensity of the porphyry is greater than that of the coal seam.In the area where the porphyry intrudes,the mining of the working face and the excavation of the roadway will reduce the speed and affect the coal mine.The overall mining ratio.For the intrusion area of porphyry,the most commonly used methods can be divided into four categories: direct hard crossing,moving and jumping,blasting and water injection softening.However,these methods have their limitations and are not suitable for all situations.For example,direct hard contact will cause the wear of the picks of the roadheader and the shearer to increase,and the cutting speed will decrease;More serious problems such as increased workload and reduced recovery rate;in the actual production process of coal mines,due to the limited construction space of the working face,only a small range of blasting can be carried out on the working face.During the blasting process,the work area is covered with rock dust,which requires high wind flow on the working face,and there are major safety hazards.The water injection softening method is greatly affected by the geological structure.With the development of microwave technology,it has been proposed to apply microwave to rock breaking.In view of the reality that the intrusion of porphyry increases the difficulty of coal mining and excavation,this paper takes the porphyry collected from Madaotou Coal Mine of Datong tong Coal Group as the research object,and uses COMSOL simulation software to analyze the electric field distribution and internal electric field Simulation of temperature distribution,using different power microwaves to treat the porphyry samples for different times,and then through a series of mechanical experiments and indoor experiments to analyze the mechanical properties of microwave-treated porphyry under different powers and different processing times.Changes in structure and distribution of surface elements,changes in mineral types and composition content.The following conclusions are obtained:(1)The COMSOL simulation software was used to simulate the internal electric field distribution and temperature distribution of porphyry under microwave irradiation.The size of the rock sample will affect the electric field distribution and the highest temperature position and the highest temperature value in the microwave heating device.The temperature change of the porphyry under microwave irradiation is inversely proportional to the size of the rock.The effect of microwave irradiation on porphyry is proportional to the input power of microwave irradiation and the action time of microwave;(2)Microwave irradiation will reduce the quality of the porphyry specimens,damage the surface structure characteristics of the porphyry specimens and even destroy the integrity of the porphyry specimens.After microwave irradiation,the quality of the porphyry specimens Decrease,in terms of macroscopic surface structure,when the input power and action time are the same,the structural change of porphyry will decrease with the increase of size,showing an inverse relationship;(3)Microwave irradiation will deteriorate the physical and mechanical properties of porphyry,which can effectively reduce the strength of porphyry specimens.The attenuation of the strength of the porphyry rock is directly proportional to the action time and input power of the microwave,and is inversely proportional to the size of the specimen of the porphyry rock;(4)Microwave irradiation will obviously increase the degree of pore development on the surface of the porphyry rock specimen,increase the surface roughness of the specimen,and destroy the surface integrity of the porphyry specimen.Scanning electron microscope(SEM)was used to observe the microstructure changes of porphyry before and after microwave irradiation with different parameters.The better the effect,the energy spectrum analysis of the selected areas of the porphyry after microwave irradiation found that the types of surface elements on the porphyry specimen did not change;(5)Microwave irradiation will not cause the mineral composition of the porphyry specimen to change,but it will affect the content of the mineral composition.Diffraction analysis of the porphyry samples by XRD and comparing the mineral types of the porphyry before and after microwave irradiation with different parameters.Quantitative analysis shows that after microwave irradiation,the content of phlogopite appears to decrease with the extension of microwave action time and the increase of microwave input power.